1. Field of the Invention
The present invention relates, in general, to a self-supporting air tube for blasting and method of blasting rock using the air tube and, more particularly, to a self-supporting air tube for blasting and method of blasting rock using the air tube that allow a pair of support wings, extending from the outside of an air bladder to the wall of the blasting hole symmetrically with respect to the longitudinal axis of the air bladder, to be supported on the wall of a blasting hole and, therefore, positions the air bladder in the center portion of the blasting hole, so that explosive loaded in the blasting hole can be uniformly distributed throughout the blasting hole, thus performing an air decking function and uniformly projecting explosive power onto the rock, and that allow weights to be accommodated in weight pockets formed below the support wings or in the lower portions of the support wings, so that the center of gravity of the air tube can be positioned at the lower portion of the air tube and, therefore, the easy insertion of the air tube into the blasting hole and the quick installation of the air tube in the blasting hole can be achieved, thus considerably shortening blasting time.
2. Description of the Related Art
In the field of rock blasting, air decking is a technology of exploding explosive while maintaining a space, which functions as a small free face, in a drilled blasting hole, thus reducing the amount of explosive used and decreasing vibration and noise generated at the time of blasting.
A representative air decking technology prevents explosive power from leaking via a blasting hole at the time of blasting by placing a plug between stemming material and explosive, as disclosed in U.S. Pat. No. 5,936,187. The plug is made of soft material, has a cap shape with stripe-shaped grooves, is inserted into a blasting hole and forms an air layer. With the representative air decking technology, the number of flying rocks and blasting noise are reduced and the degree of breakage is increased.
The technology is a technology of preventing the explosion power of explosive from leaking via blasting holes, so that the technology is disadvantageous in that it does not form air layers in blasting holes, and does not control the length of loaded explosive and expand the area onto which explosive power is projected through forming air layers.
Furthermore, in the technology, the plug may become stuck in the middle of a blasting hole at the time of fitting the plug into the blasting hole, so that it becomes technically impossible to control the amount of air in the blasting hole. The reason for this is that it is impossible to maintain a uniform drilling diameter due to the wear of the drill bit caused by the friction between the drill bit and rock.
Another decking technology is a blasting method using gasbags, which is disclosed in U.S. Pat. No. 6,213,212. The gasbag used in this technology is manufactured by separately inserting powder and liquid into the same tube so that the powder and the liquid can be easily mixed with each other at a blasting site. When the gasbag is inserted into a blasting hole at a certain location, the powder reacts with the liquid after two or three hours, so that the gasbag inflates and comes into tight contact with the wall of the blasting hole, thus forming an air layer.
However, the second air decking technology is problematic in that there are many cases where the powder and the liquid chemical component do not form the air layer even after 2 or 3 hours have elapsed. As a result the technology is disadvantageous in that the benefits of air decking are not realized in those cases and the cost thereof is high.
Still another technology is a technology of forming an air layer in a space surrounding a stake by placing a device, which is formed by resting a cap-shaped plastic plug on the stake, in the lower portion of a blasting hole or between explosives.
In order to solve the above-described problems of the conventional air decking technology, the present inventor proposed a method of blasting rock using air tubes embedded in a loaded explosive layer, in which, as shown in FIG. 1, artificial free faces are formed by inserting two or more air tubes 2 having a uniform length in a blasting hole 1, the air tubes 2 are embedded by surrounding the air tubes 2 with explosive and, thereafter, the explosive is exploded, in Preceding Korean Pat. No 10-0441222 (corresponding to U.S. Pat. No. 6,631,684, the contents of which is incorporated herein by reference it its entirety).
Unlike the existing air decking technologies, the above-described technology is a method in which air tubes, which are provided with air inlets to inject air into the air tubes and, therefore, prevent the leakage of the air and which are made of material capable of sufficiently withstanding the weight of explosive, are inserted into a blasting hole, explosive is loaded around the air tubes, and, finally, the explosive is exploded with the air tubes embedded in the explosive.
In accordance with the above-described technology, air tubes can be freely placed in the upper portion of a blasting hole, the lower portion of the blasting hole or between explosives, the amount of air can be appropriately adjusted depending on the strength of the rock, and the degree of breakage of rock can be controlled.
Furthermore, the projection area on rock near a free face is maximally increased by increasing the length of loaded explosive using the embedded type air tubes, so that the specific surface area to which explosive power is applied is enlarged and the explosive power of the explosive is used only to break the rock.
Furthermore, the length of explosion of explosive is increased due to increase in the specific surface area, so that total pressure is maximally increased in a blasting hole and rock is broken by the increased total pressure. The explosive is exploded near a free face, so that rock can be blasted using a small amount of explosive, and explosive power is distributed toward the free surface, thus reducing blasting vibration.
In the meantime, the length of a stemming material can be shortened due to the increased length of explosion of explosive, so that the occurrence of boulders can be considerably reduced.
However, in the rock blasting method using a conventional air tube embedded in a loaded explosive layer, the cases where an air tube having a diameter smaller than that of a blasting hole is inclined in the blasting hole or a lightweight air tube becomes stuck in the middle of a blasting hole occasionally occur. As a result, explosive cannot be uniformly distributed throughout the entire length of the blasting hole, so that the balance of explosive power applied to rock at the time of explosion is not kept, thus causing the occurrence of boulders.
Furthermore, to prevent an air tube from being inclined, a support frame 3 is fitted around the outside of an air tube 2 and the air tube 2 and the support frame 3 are inserted into a blasting hole, as shown in FIG. 2. Accordingly, the blasting method using the conventional air tube is disadvantageous in that installation work is inconvenient, blasting cost is increased and blasting time is lengthened.
Therefore, the present inventor proposes a self-supporting air tube for blasting and method for blasting rock using the air tube, in which the structure of the air tube is improved in such a way that a pair of support wings projecting from the outside of an air bladder symmetrically with respect to the longitudinal axis of the air bladder are integrated with the air bladder and one or more weight pockets can be attached to the lower portion of the air tube. As a result, the support wings are supported on the wall of a blasting hole and allow the air bladder to be positioned in the middle of the blasting hole, so that explosive blasts rock while being uniformly distributed throughout the blasting hole. The center of gravity of the air tube is positioned at the lower portion of the air tube due to the weight pockets attached to the lower portion of the air tube, so that the installation of the air tube in the blasting hole is facilitated and the quick installation of the air tube can be achieved, thus shortening blasting time.
That is, unlike a conventional technology in which an air tube is inclined at the time of installing the air tube in a blasting hole or in which an air tube is installed in a blasting hole using support equipment, the present invention utilizes a self-supporting air tube that is provided with a pair of support wings at the outside of an air bladder symmetrically with respect to the longitudinal axis of the air bladder, so that the air bladder is uniformly spaced apart from the wall of a blasting hole and positioned at the center of the blasting hole and the center of gravity of the air tube is positioned at the lower portion of the air tube. Accordingly, the air tube can be quickly and easily installed in a blasting hole, the explosive power of explosive is maximally distributed throughout the blasting hole due to the air tube forming an artificial free face, and the explosive power of explosive is uniformly projected onto rock at the time of explosion.
According to the above characteristics, the self-supporting tube is embedded in explosive, so that the amount of use of explosive is reduced, explosion vibration can be distributed toward an internal artificial free face, and the length of explosion of explosive can be extended up to the free face, thus considerably reducing the occurrence of boulders.
In general, general rock blasting on an open field is associated with two or three free faces, so that two or three free faces are achieved in proportion with the height of a step. Accordingly, rock can be broken in proportion to the increase in the number of free faces even though explosive power is weaker. In the case of a general rock blasting method, the explosive power of explosive is not sufficiently transmitted to rock due to a large stemming length.
However, in the method of the present invention, an air tube is embedded in explosive, so that the amount of loaded explosive can be minimized and the length of explosion of explosive can be maximized. The explosive can be loaded in the vicinity of two or three free faces with the help of the self-supporting air tubes, so that vibration is considerably reduced and the degree of breakage of rock can be considerably increased.
Meanwhile, since the drill of a drilling machine is repeatedly used at the time of drilling a blasting hole to use ANFO or Bulk type watergel explosive, there occurs a bit gage drop phenomenon in which the front part of the drill is worn away and the diameter of a drilled hole is reduced.
As a result, the amounts of loaded ANFO or Bulk type watergel explosive composed of powder are different for individual blasting holes due to the different diameters of drilled holes, so that it is technically difficult to adjust the amount of ANFO or Bulk type watergel explosive. The present invention is a scheme capable of overcoming the difference in stemming length by adjusting the length of the air tube.
It should be understood that the term “self-supporting” used in the present specification and the attached claims refers to “standing upright and being supported in a blasting hole without using special equipment” in the case of inserting an air tube into the blasting hole.